This invention relates in general to electrophotographic imaging members and, more specifically, to positively and negatively charged electrophotographic imaging members that are ambipolar or bipolar, and wherein the imaging members contain at least two of photogenerating and charge transport layers and processes for forming images on the member. More specifically, the present invention relates to a photoconductive imaging member containing a charge generation layer or photogenerating layer comprised, for example, of a photogenerating component, a charge transport component, and an electron transport component, and a second charge transport layer comprised of a charge, especially hole transport component, an electron transport component and binder. In embodiments the weight ratio of the charge transport/electron transport in the charge transport layer is preferably, for example, 3:2. Also, in embodiments there can be selected thick photogenerating layers, for example, of 8 or more microns, and more specifically, from about 5 to about 18 microns, and wherein the amount of photogenerating component can be decreased to, for example, 5 weight percent or less.
In embodiments of the present invention there are provided photoconductive imaging members comprised of a photogenerating layer of a metal free phthalocyanine component dispersed in a matrix of a resin binder, hole transporting (HT) and an electron transporting (ET) component in certain ratio amounts in, for example, ratio amounts of HT:ET from about 5:1 to about 1:2, and yet more specifically, in, for example, ratio amounts of about 4:1 to about 3:2, and thereover as a second or top layer a charge, especially hole transport layer comprised of a hole transport molecule electron transport molecules (ET), and a resin binder HT:ET range of about 5:1 to about 1:2, yet more specifically about 4:1 to about 3:2. The electrophotographic imaging member layer components, which can be dispersed in various suitable resin binders, can be of various thickness, however, in embodiments a thick layer, such as from about 5 to about 60, and more specifically from about 8 to about 12 microns, is selected for the photogenerating layer and for the charge transport layer the thickness thereof is, for example, from about 10 to about 50, and more specifically from about 10 to about 20, and yet more specifically about 10 microns. This member can be considered a dual function layer since it can generate charge and transports charge and electrons over a wide distance, such as a distance of at least about 50 microns. Also, the presence of the electron transport components in the photogenerating layer can enhance electron mobility and thus enable a thicker photogenerating layer, and which thick layers can be more easily coated than a thin layer, such as about 1 to 2 microns thick. Furthermore, there is provided in accordance with embodiments of the present invention linear and proportional filed dependent organic photoreceptors, and which members enable, for example, excellent image quality, substantially constant photoinduced discharge characteristics (PIDC) and thus minimal or substantially no variation in image quality; stable photoreceptors resulting, for example, from the use of photogenerating layers that possess linear and proportional field dependent collection efficiencies (CE); and prolonged photoreceptor wear properties.
A number of electrophotographic imaging members are multi-layered imaging members comprising a substrate and a plurality of other layers such as a charge generating layer and a charge transport layer. These multilayered imaging members also often contain a charge blocking layer and an adhesive layer between the substrate and the charge generating layer. “Plywooding” refers, for example, to the formation of unwanted patterns in electrostatic latent images caused by multiple reflections during laser exposure of a charged imaging member. When developed, these patterns resemble plywood. The multi-layered imaging members can be costly and time consuming to fabricate because of the many layers that are formed. Further, complex equipment and valuable factory floor space are usually needed to manufacture multi-layered imaging members. In addition to presenting plywooding problems, the multi-layered imaging members often encounter charge spreading which degrades image resolution.
Another problem that may be encountered with some multilayered photoreceptors comprising a charge generating layer and a charge transport layer is that the thickness of the charge transport layer, which is normally the outermost layer, tends to become thinner due to wear during image cycling. The change in thickness causes changes in the photoelectrical properties of the photoreceptor. Thus, to maintain image quality, complex and sophisticated electronic equipment and software management are usually necessary in the imaging machine to compensate for the photoelectrical changes, which can increase the complexity of the machine, cost of the machine, size of the footprint occupied by the machine, and the like. Without proper compensation of the changing electrical properties of the photoreceptor during cycling, the quality of the images formed can degrade because of spreading of the charge pattern on the surface of the imaging member and a decline in image resolution. High quality images can be important for digital copiers, duplicators, printers, and facsimile machines, particularly laser exposure machines that demand high resolution images. Moreover, the use of lasers to expose conventional multilayered photoreceptors can lead to the formation of undesirable plywood patterns that are visible in the final images.
There have been attempts to fabricate electrophotographic imaging members comprising a substrate and a single electrophotographic photoconductive insulating layer in place of a plurality of layers such as a charge generating layer and a charge transport layer. However, in formulating single electrophotographic photoconductive insulating layer photoreceptors several problems may need to be addressed including charge acceptance for hole and/or electron transporting materials from photoelectroactive pigments. In addition to electrical compatibility and performance, a material mix for forming a single layer photoreceptor should possess the proper rheology and resistance to agglomeration to enable acceptable coatings. Also, compatibility among pigment, hole and electron transport molecules, and film forming binder is desirable.